The present disclosure relates generally to wireless communications, and more particularly, to coordinated multipoint (CoMP) uplink (UL) reception and related network nodes.
Coordinated Multipoint (CoMP) transmission/reception is an advanced technology for cellular communication networks to improve coverage, support high data rates, improve cell-edge throughput and/or to increase system throughput.
Uplink CoMP generally implies coordination/cooperation among multiple geographically separated reception points, and downlink CoMP generally implies dynamic coordination/cooperation among multiple geographically separated transmission points. In general, the basic idea of CoMP is to perform joint detection in the uplink by jointly processing radio signals received at multiple points, and likewise to perform joint transmission in the downlink by coordinating transmission from multiple points to one or more user terminals.
As an intermediate step towards general CoMP operation, so-called intra-site coordination/cooperation has been proposed, where different sectors of the same radio base station are coordinated.
It is also possible to coordinate different sectors belonging to different sites, so-called inter-site coordination/cooperation, where the data has to be exchanged between the involved radio base stations, or more generally access points, via the so-called backhaul network.
For the uplink, the entity responsible for decoding, typically one of the access points such as a serving radio base station, may thus collect samples from other access points via the backhaul network, and include them in the decoding of the user. CoMP is discussed, for example, in International Publication No. WO 2014/062104 entitled “Selection of Access Points For Coordinated Multipoint Uplink Reception,” the disclosure of which is hereby incorporated herein in its entirety by reference.
The area of coordination/cooperation between base stations (e.g., eNBs) is of high interest to increase capacity and coverage, especially in Hetnet (heterogeneous network) scenarios. Most solutions and features so far are intra-eNB, as they are easier to deploy with, for example, common baseband processing and/or good interconnect between processing boards. Coordination/cooperation between different base stations, however, may be needed to work with current transport network deployments.
One coordination feature that is useful in the above scenario to improve uplink reception by coordinated multi-point (CoMP) reception. The idea is to receive the signal from one wireless device UE at several reception points, and to utilize the received signals from all of these points to improve reception. One approach, for example, uses maximal ratio combining (MRC) and/or interference rejection combining (IRC) on the received signals from the different reception points. Another approach is to demodulate and decode the signal at each of the reception points, and then it may be sufficient that the received signal quality is good enough at one of the reception points to recover the information sent by wireless device UE. This is known as soft handover in WCDMA networks. Also, intermediate data, for example, soft values and/or coded bits may be exchanged between the reception points.
Existing approaches for CoMP may rely, to a great extent, on availability of a low-latency, high-throughput link between cooperating cells or base stations. For example, in the intra-eNB case, IQ samples received for several cells of the same base station can be processed jointly using common baseband processing. Then, if a wireless device UE is located on the cell edge, IQ samples from the neighbor cell can be used to improve reception performance.
In the inter-eNB case, a similar approach can be used between cells in different base station, for example, by providing centralized baseband processing for all base stations or for a group of adjacent base stations. Centralized baseband processing may require fast links (e.g., Common Public Radio Interface or CPRI) typically on dedicated fiber connections between each base station and the centralized baseband processor.
Another approach for inter base station CoMP (e.g., inter-eNB CoMP) would be to keep the baseband processing in each base station while providing high bandwidth and low latency transport network between base stations. This would allow sending, for example, IQ samples received for a cell in a cooperating base station over the transport network to a serving base station. The serving base station could then use UpLink (UL) CoMP for multiple cells including the cell in the first base station similar to the centralized baseband processing solution. Stated in other words, the serving base station could perform joint baseband processing using IQ data (also referred to as IQ samples) from the serving base station and from an adjacent base station(s) to provide UL CoMP.
For CoMP to be fully flexible (that is, to not put significant constraints on scheduling) in LTE, scheduling decisions may need to be distributed from the serving base station to the cooperating base station, and arrive before wireless device UE start the scheduled UL transmission. To get the most from CoMP, the information from the reception in the cooperating base station may need to arrive at the serving base station before it schedules the next transmission, and sufficient processing time may be required at both cooperating and serving base stations.
In traditional network deployments, the transport network may have constraints on bandwidth and/or it may have high latency. The constraints on bandwidth may limit a type of CoMP that can be employed, because high latencies may constrain scheduling and/or reduce achievable gains due to information arriving late. Accordingly, decentralized CoMP may be difficult use with conventional transport networks. A significant restriction may be that synchronous HARQ is used in the uplink which means that retransmissions may be required to occur on predefined occasions. This may set a limit on available processing time at the base station. Accordingly, a high-latency low-bandwidth X2 link may reduce performance of conventional UL CoMP.